Problem: Evaluate the following expression when $a = 5$ and $b = 4$. $3$ $a$ $ + 6$ $b$ $ - 8$
Solution: Substitute $5$ for ${a}$ and $4$ for ${b}$ $ = 3{(5)} + 6{(4)} - 8 $ $ = 15 + 24 - 8 $ $ = 31$